Edged medical cutting tool

ABSTRACT

[Problem] To provide a medical cutting tool with low impalement resistance. [Solution] The edged medical cutting tool comprising a knife, trocar or cutting suture needle has a sharp edge ( 1 ) for incising living tissue and a flat part ( 2 ) that configures the edge, and the color of the portion of the flat part ( 2   a ) along the edge ( 1 ) differs from the color of the rest of the flat part ( 2   b ). The difference in color results from a difference in the thickness of an oxide film. Another edged medical cutting tool is configured of austenite stainless steel and has a sharp edge ( 1 ) for incising living tissue and a flat part ( 2 ) that configures the edge. The chrome content of the portion of the flat part ( 2   a ) along the edge is higher than the chrome content of the rest of the flat part ( 2   b ).

TECHNICAL FIELD

The present invention relates to a sharply-edged medical cutting toolfor incising a biological tissue with an improved piercing property.

BACKGROUND

At the time of an ophthalmic surgical operation, a knife or trocar isemployed to pierce an eyeball or incise a cornea or sclera, and a sutureneedle for piercing or incising a muscle or a skin is employed to suturean affected area. A medical cutting tool such a knife, a trocar, or asuture needle includes a sharp tip, a sharp edge elongated from thesharp tip, a plane portion that forms the edge, and a body portioncontinuously elongated from the plane portion.

The edge and the plane portion have cross sections having a polygonalshape such as a triangle, a rectangle, or a pentagon. The shape of thecross section is set according to a type of a desired medical cuttingtool, that is, according to whether the medical cutting tool is a knife,a trocar, or a suture needle. In addition, regardless of thecross-sectional shape of the medical cutting tool, two edges are formedby using the sharp tip as a starting point (for example, see PatentLiterature 1).

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 06-077313

SUMMARY OF INVENTION Technical Problem

In the medical cutting tool having the aforementioned configuration, itis necessary to reduce impalement resistance generated during theincision of the affected area. For example, if the impalement resistanceis large, a doctor may feel fatigued, and may not accurately perform asurgical operation. For this reason, a manufacturer of a medical cuttingtool has an important issue to improve a medical cutting tool includinga knife, a trocar, and a suture needle having reduced impalementresistance.

The present invention provides an edged medical cutting tool havingreduced impalement resistance.

Solution to Problem

In order to address the aforementioned problem, the inventors have mademany development experiments. As a result, the inventors have found afact that the impalement resistance is reduced by providing a sharpedge. In addition, the inventors have recognized that the sharp edge canbe implemented by performing an electrolytic polishing process or achemical polishing process within a short time after a polishingprocess.

The inventors have also recognized that a color of one plane portionalong the edge is different from that of the other plane portion whenthe sharp edge is configured by performing an electrolytic polishingprocess or a chemical polishing process and the polishing process isperformed within a short time. Furthermore, the inventors have alsorecognized that the chromium content of one plane portion along the edgeis different from that of the other plane portion when a stainless steelis employed as a material.

According to an aspect of the present invention, there is provided amedical cutting tool including: a sharp edge for incising a biologicaltissue; and plane portions that form the edge, wherein a color of oneplane portion along the edge is different from that of the other planeportion.

In the edged medical cutting tool described above, a color differencebetween one plane portion along the edge and the other plane portion isbased on a thickness difference of an oxide film.

According to another aspect of the present invention, there is providedan edged medical cutting tool made of an austenitic stainless steel,including: a sharp edge for incising a biological tissue; and planeportions that form the edge, wherein a chromium content of one planeportion along the edge is larger than a chromium content of the otherplane portion.

Advantageous Effects of Invention

In the edged medical cutting tool (hereinafter, simply referred to as acutting tool) according to the present invention, it is possible toreduce impalement resistance by forming a sharp edge. Therefore, duringan ophthalmic surgical operation or a general surgical operation, it ispossible to alleviate fatigue of a doctor and accurately perform theincision.

Particularly, since the formation of the sharp edge can be recognized bychecking a color difference between one plane portion along the edge andthe other plane portion out of the flat portions that form the edge ofthe cutting tool, it is possible to perform accurate inspection at leastwhen the cutting tool is manufactured.

In addition, in another cutting tool according to the present invention,by comparing the chromium content of one plane portion along the edgewith the chromium content of the other plane portion, it is possible tocheck whether or not the sharp edge is formed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a trocar as a cutting tool according toan embodiment.

FIG. 2 is a photographic image of the trocar illustrated in FIG. 1.

FIG. 3 is a photographic image illustrating sampling positions whenmaterial components of a trocar are quantitatively analyzed.

FIG. 4 is a photographic image illustrating sampling positions whenmaterial components of a trocar as a comparative example arequantitatively analyzed.

REFERENCE SIGNS LIST

-   -   A: TROCAR    -   1: EDGE    -   2, 2 a, 2 b: PLANE PORTION    -   3: RIDGE    -   4: SHARP TIP    -   5: BODY PORTION    -   6: BOUNDARY    -   7: SMALL PLANE PORTION    -   10: DASHED-DOTTED LINE (boundary between the plane portion 2 a        and the other plane portion 2 b)

DESCRIPTION OF EMBODIMENTS

Hereinafter, a cutting tool according to the present invention will bedescribed. According to the present invention, when a biological tissueis pierced and incised during a surgical operation using a knife, atrocar, an edged suture needle, and the like, impalement resistance isreduced, so that it is possible to alleviate fatigue of a doctor andaccurately perform the surgical operation.

According to the present invention, a sharp edge for incising abiological tissue is configured by causing two planes to intersect eachother. In addition, a color of one plane portion along the edge isdifferent from that of the other plane portion. This color differencecorresponds to a thickness difference of an oxide film, which is causedby reducing a processing time in an electrolytic polishing process or achemical polishing process (electrolytic polishing or the like)performed during a cutting tool manufacturing procedure.

In other words, since burrs attached to the edge are large in the caseof a medical cutting tool manufactured in the related art, it isnecessary to perform an electrolytic polishing or the like for a longtime in order to remove the burrs from the edge. In addition, due to thelong-time electrolytic polishing or the like, elution also occurs in aportion along the edge when the burrs attached to the edge are removed.As a result, fine roundness is generated at a pointed end of the edge,so that sharpness of the edge disappears.

On the contrary, in a procedure of manufacturing a cutting toolaccording to the present invention, the burrs attached to the edge areremoved by using short-time electrolytic polishing or the like, so thata sharp edge can be implemented. In addition, as a result of theshort-time electrolytic polishing or the like, a thickness difference ofan oxide film occurs between one plane portion along the edge and theother plane portion, and a color difference occurs due to the thicknessdifference of the oxide film.

In the cutting tool where a color difference occurs between one planeportion along the edge and the other plane portion as described above, achange in material component also occurs in addition to the colordifference.

Therefore, the cutting tool according to the present invention can berecognized by the color difference between one plane portion along theedge and the other plane portion or by quantitatively analyzing thematerial components.

Furthermore, in the cutting tool according to the present invention, itis possible to sufficiently reduce the impalement resistance incomparison with that of the cutting tool typically used in the relatedart.

As a material for the cutting tool according to the present invention, ametal represented by a carbon steel or a martensitic stainless steelwhich can be expected to be hardened through thermal treatment or anaustenitic stainless steel which cannot be expected to be hardenedthrough thermal treatment can be selectively used. In addition, it ispreferable that the cutting tool according to the present invention beconfigured by performing a shaping process and a hardening process for adesired cutting tool through processes optimized to the selectedmaterial.

Next, a trocar A according to the present embodiment will be describedwith reference to FIGS. 1 and 2. The trocar A illustrated in FIGS. 1 and2 is a cutting tool for piercing an eyeball and cutting a cornea orsclera in an ophthalmic surgical operation. As a material of the trocarA, SUS302 that is an austenitic stainless steel is employed. The trocarA is formed in a round bar shape having a fiber-like extending structureby performing a cold drawing process on an element wire with apredetermined area reduction rate and having a high strength through afabrication and hardening process.

In addition, the trocar A is configured in a straight needle shape byperforming a press process and then performing a grinding process on anend portion of the round-bar-shaped material fabricated as describedabove or by directly performing the grinding process on the end portion.Incidentally, as the cutting tool according to the present invention, inaddition to the trocar A according to the present embodiment, there arean edged suture needle, a knife, and the like having a cuttingfunctionality and any of them may be formed in the configuration of thetrocar A described below.

In FIGS. 1 and 2, the trocar A includes a pair of sharp edges 1 formedby causing two plane portions 2 including a plane portion 2 illustratedin FIG. 1 and a plane portion (not illustrated) on the rear side of thepaper of FIG. 1 to intersect each other. Particularly, in the trocar Aaccording to the embodiment, a cross section (a transverse cross sectionof a portion where the edge 1 of the trocar A exists) of a portioncorresponding to the edge 1 is formed in a rhombus shape. The pair ofedges 1 are formed on the two sides in the width direction (in the arrowdirection X in FIG. 1), and the pair of ridges 3 having no incisingfunction are formed on the two sides in the thickness direction(direction perpendicular to the paper plane of FIG. 1) perpendicular tothe width direction. In addition, the rear surface side of the trocar Aillustrated in FIG. 1 has the same shape as that illustrated in FIG. 1.

The edge 1 and the plane portion 2 are formed to converge toward a sharptip 4. In other words, the edge 1 and the plane portion 2 are inclinedby using the sharp tip 4 as a starting point. Therefore, the pair ofedges 1, the pair of ridges 3, and the plane portions 2 that forms theedges 1 and the ridges 3 are separated from each other according to therespective inclination and are connected to the body portion 5. The bodyportion 5 is formed in a round bar shape having a predetermineddiameter, so that the trocar A is formed in a straight needle shape.

In the trocar A having the aforementioned configuration, as the planeportion 2 that forms the edge 1 is separated from the edge 1 and isconnected to the body portion 5, a boundary 6 is formed between theplane portion 2 and the body portion 5. The boundary 6 forms an edgehaving an obtuse angle by causing the plane portion 2 and the outercircumferential surface of the body portion 5 to intersect each other.

In addition, in the trocar A according to the present embodiment, asmall plane portion 7 is formed on the sharp tip 4 sides of the twoplane portions 2 formed on one side in the thickness direction. Byforming the small plane portion 7, the sharp tip 4 is configured fromthree planes including the two plane portions 2 and the small planeportion 7. Therefore, the sharp tip 4 is formed necessarily as onepoint, so that it is possible to improve positioning accuracy at thefirst time of impalement of a tissue and reduce the impalementresistance.

As illustrated in FIG. 2, a part of the plane portions 2 along the edge1, that is, a plane portion 2 a (one plane portion 2 a) formed betweenthe dashed-dotted line 10 and the edge 1 illustrated in FIGS. 1 and 2has a color different from that of the other plane portion 2 b. However,since it is difficult to clearly represent the color difference betweenthe plane portions 2 a and 2 b by using a certain line as a boundary,the dashed-dotted line 10 indicates the boundary between the planeportion 2 a and the other plane portion 2 b for convenience purposes.

The inventors of the present invention have examined the cause of thecolor difference, and it have been determined that the color differenceis generated due to a thickness difference of an oxide film between theplane portions 2 a and 2 b. In other words, since the oxide film in theplane portion 2 a is thin, the color is relatively close to a color of ametal material. Since the oxide film in the plane portion 2 b is thick,the color is close to gold. Incidentally, in the photographic image ofFIG. 2, the plane portion 2 a has a dark color, and the plane portion 2b has a white color. However, these color components are caused fromillumination during the photographing.

As illustrated in FIG. 2, the plane portion 2 a having a different coloris formed in a part of the plane portion 2 along the edge 1, a portionalong the boundary 6, and a portion along the ridge 3. In other words,the plane portion 2 a is formed over the substantially entire area inthe vicinity of the plane 2. However, in the case of the cutting tool,if the plane portion 2 a having a color different from that of the otherplane portion 2 b is formed in a part of the plane portions 2 along theedge 1, it is possible to sufficiently reduce the impalement resistance.

Next, a procedure of manufacturing a trocar A capable of removing burrsattached to the edge 1 by using a short-time electrolytic polishing orthe like will be described in brief.

As described above, the trocar A is formed as a rod-like material bycutting a round bar material, which is made of an austenitic stainlesssteel having a predetermined strength through a cold drawing process, bya desired length. Then, by performing a press process on the end portionon the one side of the material, the cross section is formed in arhombus shape. The formed portion is ground to form a plane portion 2,so that an edge 1 is formed in an intersection between the two planeportions 2. Furthermore, a ridge 3 is formed by an intersection portionbetween the two plane portions 2 or by a press-processed surface, and aboundary 6 is formed in an intersection between one plane portion 2 andthe outer circumferential surface of the body portion 5.

Similarly to the aforementioned case, when the material is ground, burrsare inevitably attached to the edge 1, the ridge 3, and the boundary 6between the plane portion 2 and the body portion 5. Therefore, byreducing at least the burrs attached to the edge 1, it is possible toremove the burrs through a short-time electrolytic polishing process orthe like. In this manner, in order to reduce the attached burrs, aprocessing rate during the grinding process is reduced.

The reduction of the processing rate can be implemented by decreasing aload to the material during the grinding process. For example, if aprocessing rate at the time of grinding is set to about 1/10 of theprocessing rate at the time of grinding of the trocar in the relatedart, the burrs attached to the edge 1 can be sufficiently reduced.However, the processing rate is not limited to a specific value, but itmay be appropriately set depending on a target cutting tool.

When the burrs attached to the edge 1 are reduced by reducing theprocessing rate at the time of grinding, the burrs can be removed withina short time by performing a polishing process such as an electrolyticpolishing. As a result, it is possible to reduce a processing time ofthe electrolytic polishing or the like. As the processing time of theelectrolytic polishing or the like is reduced, the polishing is notuniformly performed on the plane portion 2, but irregularity occurs inthe polishing process. In other words, a difference is generated in adegree of polishing between the plane portion 2 a along the edge 1 andthe other plane portion 2 b.

The partial difference in a degree of polishing in the plane portion 2is caused from a thickness difference in an oxide film, a difference ina material component, and a difference in surface roughness. In otherwords, since the material is thin in the plane portion 2 a along theedge 1, the electrolytic polishing or the like progresses at a highspeed, so that the elution amount of iron increases and the chromiumcontent increases. Therefore, the oxide film thereof becomes thin, andthe surface roughness is reduced. On the contrary, in the other planeportion 2 b, since the material is thick in comparison with the planeportion 2 a, the electrolytic polishing or the like is performed at alow speed in comparison with the plane portion 2 a, so that the elutionamount of iron decreases and the chromium content decreases. Therefore,the oxide film thereof becomes thick, and the surface roughnessincreases.

In this manner, the color of plane portion 2 a along the edge 1 isdifferent from that of the other plane portion 2 b due to a thicknessdifference of an oxide film, so that the chromium content of the planeportion 2 a is larger than the chromium content of the plane portion 2b.

Next, the description will be made for a result of the comparisonbetween the trocar A according to the present embodiment and the trocarin the related art (comparative example). FIG. 3 is a diagramillustrating the trocar A according to the present embodiment andsampling positions for quantitative analysis of metal components. FIG. 4is a diagram illustrating the trocar according to the comparativeexample and sampling positions for quantitative analysis of metalcomponents. Spectra 1 to 5 are arranged on the flat portion along theedge, and spectra 6 to 10 are arranged on the other plane portion.

According to the present embodiment, an electrolytic polishing processwas performed for the material subjected to the planar grinding. Theelectrolytic polishing was performed such that the entire length of theplane portion 2 was immersed for about 35 seconds, and then, the lengthportion corresponding to the edge 1 was immersed for about 5 seconds.Through the electrolytic polishing process, all the burrs attached tothe edge 1 were removed. After the electrolytic polishing was completed,the quantitative analysis using X-ray analysis was performed for thespectra 1 to 10.

As a result, in the spectrum 1, the chromium content was 31.38%; theiron content was 60.08%; and the nickel content was 8.64%. In addition,in the spectrum 2, the chromium content was 31.45%; the iron content was59.36%; and the nickel content was 9.19%. In addition, in the spectrum3, the chromium content was 31.75%; the iron content was 60.10%; and thenickel content was 8.15%. In addition, in the spectrum 4, the chromiumcontent was 29.10%; the iron content was 61.33%; and the nickel contentwas 9.57%. In addition, in the spectrum 5, the chromium content was28.035%; the iron content was 63.41%; and the nickel content was 8.56%.

In the spectrum 6, the chromium content was 26.55%; the iron content was63.57%; and the nickel content was 9.88%. In addition, in the spectrum7, the chromium content was 26.47%; the iron content was 63.17%; and thenickel content was 10.36%. In addition, in the spectrum 8, the chromiumcontent was 28.49%; the iron content was 61.47%; and the nickel contentwas 10.04%. In addition, in the spectrum 9, the chromium content was27.40%; the iron content was 62.32%; and the nickel content was 10.28%.In addition, in the spectrum 10, the chromium content was 25.07%; theiron content was 65.16%; and the nickel content was 9.77%.

From the result described above, it can be said that the chromiumcontent of the plane portion 2 a along the edge 1 is larger that that ofthe other plane portion 2 b (the spectra 6 to 10). Particularly, it isconceived that, in the spectra 1 to 3, since the thin edge 1 is formedonly by the two plane portions 2, the elution amount of iron increases,so that the chromium content increases (31.38%, 31.45%, and 31.75%). Itis conceived that, in the spectra 4 and 5, since the four plane portionsapproach each other, the relatively thick edge 1 is formed, so that theelution amount of iron is reduced and the chromium content is reduced(29.10% and 28.035%).

Here, out of the plane portion 2 a, the chromium content (31.38%) of thespectrum 1 as a portion where the thin edge 1 is formed only along thetwo plane portions 2 and the chromium content (26.55%, 26.47%, 28.49%,27.40%, and 25.07%) of the spectra 6 to 10 were compared. As a result,there were differences of 4.83%, 4.91%, 2.89%, 3.98%, and 6.31%,respectively.

In summary, it can be concluded that the chromium content of the portion(positions of the spectra 1 to 3, particularly, the width range within40 μm in the vertical direction of the edge 1) where the thin edge 1 isformed only along the two plane portions 2 out of the plane portion 2 ais larger than the chromium content of the pointed end portion(positions of the spectra 4 and 5) where the four plane portionsapproach each other. In addition, it can be concluded that the chromiumcontent of the portion (positions of the spectra 1 to 3) is obviouslylarger than the chromium content of plane portion 2 b (particularly, theportion separated by 100 μm or longer in the vertical direction of theedge 1).

Next, in the comparative example, the electrolytic polishing process wasperformed by immersing the entire length of the plane portion for about50 seconds with an electric current density higher than that of theaforementioned embodiment. Through this electrolytic polishing process,overall burrs attached to the edge were removed. After the electrolyticpolishing was completed, the quantitative analysis was performed as inthe embodiment.

As a result, in the spectrum 1, the chromium content was 27.70%; theiron content was 62.28%; and the nickel content was 9.02%. In addition,in the spectrum 2, the chromium content was 27.55%; the iron content was62.47%; and the nickel content was 8.98%. In addition, in the spectrum3, the chromium content was 26.55%; the iron content was 63.13%; and thenickel content was 9.32%. In addition, in the spectrum 4, the chromiumcontent was 25.86%; the iron content was 62.95%; and the nickel contentwas 10.19%. In addition, in the spectrum 5, the chromium content was25.22%; the iron content was 65.32%; and the nickel content was 9.46%.

In addition, in the spectrum 6, the chromium content was 25.87%; theiron content was 64.42%; and the nickel content was 9.71%. In addition,in the spectrum 7, the chromium content was 25.12%; the iron content was65.00%; and the nickel content was 9.88%. In addition, in the spectrum8, the chromium content was 25.79%; the iron content was 64.53%; and thenickel content was 9.68%. In addition, in the spectrum 9, the chromiumcontent was 24.99%; the iron content was 65.16%; and the nickel contentwas 9.85%. In addition, in the spectrum 10, the chromium content was26.26%; the iron content was 63.89%; and the nickel content was 9.85%.

In the comparative example described above, the electrolytic treatmenttime was sufficiently long, and the electrolytic polishing was performeduniformly over the entire area of the plane portion. Therefore, theelution amount of iron was also substantially uniform, and the chromiumcontent was also substantially uniform.

In addition, in the plane portion along the edge in the comparativeexample, the chromium content of the portions (positions of the spectra4, 5 and the like in the comparative example) where a thin edge isformed only along the two plane portions and the chromium content of thepointed end portions (positions of the spectra 1, 2 and the like in thecomparative example) where the four plane portions approach each otherwere compared. As a result, the former portions were 25.86% and 25.22%,and the latter portions were 27.70% and 27.55%. On the contrary to thepresent embodiment, the portions where a thin edge was formed only alongthe two plane portions tended to be slightly small.

In the trocar A according to the present embodiment, the surfaceroughness of the plane portion 2 a along the edge 1 and the surfaceroughness of the other plane portion 2 b were measured. As a result, theaverage surface roughness of the plane portion 2 a was Ra 2.38, and theaverage surface roughness of the plane portion 2 b was Ra 3.15. It canbe said that this difference is a significant difference in a medialcutting tool.

Next, an experiment of comparing impalement resistance between thetrocar A according to the embodiment and the trocar (FIG. 4) accordingto the comparative example was performed. In this experiment, similar toa typical impalement experiment for a knife, a trocar, or a sutureneedle, a force for piercing a Porvair having a thickness of 0.45 mm wasmeasured. Five samples of the trocar A and five samples of the trocaraccording to the comparative example were prepared. For each sample, thePorvair was pierced three times, and the average piercing force wasobtained. In addition, the average value of overall piercing forces(that is, piercing of 15 times) was obtained, and comparison thereof wasperformed.

As a result, for the trocar A according to the present embodiment, theaverage impalement resistance was 96.6 mili-newton (mN), the maximumvalue of impalement resistance was 107.0 mN, and the minimum value ofimpalement resistance was 78.0 mN. On the contrary, for the trocaraccording to the comparative example, the average value of impalementresistance was 139.4 mN, the maximum value of impalement resistance was158.3 mN, and the minimum value of impalement resistance was 118.3 mN.

In this manner, it can be said that the impalement performance of thetrocar A according to the present embodiment is sufficiently improved incomparison with the impalement performance of the trocar in the relatedart or the trocar according to the comparative example.

INDUSTRIAL APPLICABILITY

The present invention can be usefully applied to a thinned knife, atrocar, or an edged suture needle used in an ophthalmic surgicaloperation or a neurosurgical operation.

1. A medical cutting tool comprising: a sharp edge for incising abiological tissue; and plane portions that form the edge, wherein acolor of one plane portion along the edge is different from that of theother plane portion.
 2. The medical cutting tool according to claim 1,wherein a color difference between one plane portion along the edge andthe other plane portion is based on a thickness difference of an oxidefilm.
 3. An edged medical cutting tool made of an austenitic stainlesssteel, comprising: a sharp edge for incising a biological tissue; andplane portions that form the edge, wherein a chromium content of oneplane portion along the edge is larger than a chromium content of theother plane portion.